Absorption refrigeration system



June 23; 1942.- w. R. MCGINNIS 2,287,441

ABSORITIONA REFRIGERATION SYSTEM Filed June 13, 1939 2 Sheets-Sheet l @vue be Zim.. wle g {mm/EAV A9 @f am Gttorneus mm mv O JEZS Filed June 13, 1939 2 Sheets-Sheet 2 g m@ @mi Q .Tttoruegs Patented June 23, 1942 ABSORPTKION REFRIGERA'IION SYSTEM Walter R. McGinnis, York, Pa., assignor to York Ice Machinery Corporation, York, Pa., a. corporation of Delaware Application June `13, 1939, Serial No. 278,949

13 claims. (cl` sz-s) This invention relates to refrigeration systems, and particularly to systems of the absorption type utilizing a volatile refrigerant, such as ammonia,'and a volatile solvent, such as water.

Systems of this type have been in use for many years and were used for furnishing refrigeration where a heat source such as exhaust steam was available. Although systems of the prior art are quite flexible in operation, every change inrefrigerating load required certain adjustments to be made manually'and with considerable accu-v racy, in order to obtain eilicient operation. It is the purpose of this invention to avoid this characteristic, provide a system which is automatically responsive to changes in load without ma' terial loss of efficiency, and at the same time simplify the apparatus required. Broadly stated. the apparatus comprises the usual elements such as generator, condenser, receiver, evaporator, absorber, heat exchangers, and strong aqua pump, but includes a bubble tower in place of the usual analyzer, dehydrator or equivalent device. Whereas in most prior art systems it is necessary to make use of a so-called analyzer for reducing the heat load on the generator and for reducing the temperature and water content of the vapor, and a dehydrator for separating the water vapor from the ammoniaas it is given off from the generator, the present invention contemplates the use of a single element in the form of a bubble tower for performing these and added functions. By the use of this bubble tow,-

er, the apparatus is simplied, its exibility increased, steam consumption reduced, and automatic control in response to widely and rapidly varying load conditions made possible. y

In the apparatus of the prior art it has been practically impossible to prevent the transfer of substantial quantities of water to the evaporator,

Awhich water necessitated the developing of lower suction pressure in the system to accomplish the same refrigeration, and required frequent purging to remove such water. 'I'he new system substantially avoids delivery of water to the' evapbubble tower,'by the addition-of a dual strong aqua return from the absorber, one branch 'of which delivers to the generator while the other branch delivers a limited quantity of strong aqua to an intermediate point inthe bubble tower; by the return of a limited quantity of liquid anhydrous ammonia to the tcp of the bubble tower from' the condenser, and by other refinements which will be pointed out.

As a result of this arrangement, the gas leaving the generator is cooled so `as to approximate the condensing temperature, and the amomnia gas is so effectively dehydrated that the ammonia entering the condenser is freed of water to a much greater degree than has been possible with apparatus of theprior art. In the functioning of this improved mechanism the liquid anhydrous ammonia condenses the waterfvapor outaqua fed to the bubble tower performs the func.

tion of desuperheating the vapors passingl upwardly through the tower from the generator.

The strong aqua fed tothe heater elements assists the flow of aqua in the generator by exerting an ejector pump action.

The main effect of the present invention is, therefore, to simplify the operation of thesystem.' causing it to adjust itself automatically to -changing load conditions in such manner that it is inherently stable, and otherwise to improve the eiilciency of, and reduce the 'number of parts required in absorption systems.

Whereas in prior art apparatus a substantial change in load on vthe system necessitated a manual readjustment of generator aqua load, and aqua level in the strong aqua tank to meet changing conditions, the present system compensates automatically by maintaining the proper ratio between the aqua and vapor, thus permit- `ting a mere change in steam ow to meet the new load conditions tem.

The invention will be explained in connection with the accompanying drawings, jin which:

Figure 1 is a flowsheet indicating the layout of'one embodiment-of the present invention.;

without unbalancing the sys- Figure 2 is an enlarged diagrammatic detail l ofthe bubble tower, 'generator,vcondenser and receiver shownin Figure 1; and

Figure 3 is a sectional view showing the details of the bubble vplates employed in the bubble tower illustrated. i

Figure 1 ofthe drawings shows a typical layout embodying the present invention as applied to an absorption system of the ammonia-water type. As illustrated, it includes conventional components such as a generator G, condenser C,

' surge drum 5 adapted to 'contain a strong solution of ammonia gas in water, this drum being connected to the strong aqua return 8 vapor outlet 1 and weak aqua outlet 8. Connected to the surge drum in parallel relation with one another are a plurality of heater units or calandrias,` preferably of the shell and` tube type, adapted to be supplied with a heating medium, such as steam, from a header 8. Each of these calandrias comprises a shell or casing II having a top header connected by a horizontal tube I2 to the drum 5, and a bottom header connected through a pipe I3 to a vertical pipe I4 leading into the bottom of the surge drum. The arrangement is such (see Fig.` l) that the ammonia-water solution in the drum may circulate from the drum 5 downwardly through pipe Ill, horizontally through pipe and header I3, up through the tubes I5 and back to the surge drum through the pipe I2. Steam supplied through the header 8 passes into the casing II in contact with the outer surface of the tubes I5 and ows out to a common condensate return `header I8. The heat delivered by this steam and controllable by valves I1 induces a thermal circulation through each calandria, and the vapor-,produces a gas lift to increase the circulation.

The liquid level in drum` 5 is above the upper tube sheets of the calandrias, and cross baiiles Il! (see Fig. 2) partially segregate different portions of the drums associated with the various calandrias.

In order to prevent gas locks inthe calandria's,

caused by failure of the tubes to prime, there is provided a common strong aqua header I8 fed by the return from the strong aqua pump and this header has a plurality of connections I 8, one leading to each of the pipes I3 under the control of a. manually operable valve 2|. These valves 2| control the ilow of strong aqua under pressure to nozzles 20 which direct jets into the throats 22 and thus stimulate circulation through the corresponding calandria. It will be under- .stood that although only three calandrias are shown in Fig. 2, it is possible, according to the present invention, to use any desired number of these units in parallel, and the operation is such that the concentration vof the solution in the surge drum 5 decreases progressively fromithe strong aqua return end connected to pipe 6 Where it is a maximum to the opposite end o f the drum where the weak aqua is discharged for return to the absorber. Increasing amounts of aqua are fedto the heaters through valves 2l from the strong end to the weak end of the drum, so that the circulating rates are approximately uniform and uniform high heat transfer rates are secured.

The end of the surge drum 5 adjacent the weak aqua discharge 8 embodies a. liquid level responsive float 85 disposed in a chamber 8| having a connection 81 to the top of the surge drum and a similar connection 8l to the boteach of the calandrias may be controlled individually by means ot vthe control valves I1. The drip valves 23 are normally wide open, line Il being connected to a suitable steam trap: (not shown). Similarly, the injectors 22 may be controlled by manipulationl of the valves 2l in order to proportion the circulation in the various heaters or calandrias to control the heat transfer rates as above suggested..

In accordance with the principles underlying the present invention, the, vapor outlet 1 from the surge drum 5 of the generator leads to a space 42 in the bottom of a bubble tower T embodying a plurality of bubble plates adapted to carry a shallow body of liquid through which upwardly passing vapor must pass before it is discharged to the condenser. Although various types of bubble tower might be utilized for this purpose, the tower illustrated is in principle satisfactory.v This tower T comprises an upright casing or shell 2l, closed at the top and bottom by heads 25 and 28, respectively. The bottom head 28 contains a strong aqua discharge connection 8 leading to the surge drum 5, while the top head 25 contains an ammonia vapor discharge pipe 21 leading directly to the top of the condenser C, as shown in Fig. 1. The bottom of the tower T must be at such height that gravity flow to the surge drum 5 will occur. (See Fig. 2.)

The internal structure of the bubble tower will be best understood by reference to Figs. 2 and 3, where reference character 28 designates a. plate sealed to the walls of the shell 24 and having a liquid discharge pipe 28 for permitting the flow of liquid to the next lower level, the pipe being trapped at its lower end in a cup III in which it dips below the liquid bath. The plate `28 is perforated as at 3| and this perforation is surrounded by a tubular upstanding rim or flange 32 which cooperates with the depending flange I8 of an inverted cup or bell 24 associated with each of the openings II. The bell Il is secured fn the rim 32 by means of a strap 3l and a bolt Il. The depending flange Il is serrated in such a way that gas escape openings are provided below the minimum level of liquid on the plate 28 maintained by upstanding ange I1 of the cup at the top of the pipe 28.

U The result of this arrangement is that when llquid ilowsonto the plate 28 from a cup III, it accumulates to a level denned by the ange 81, and when above that level, some liquid is caused to discharge through the pipe 29 to the bubble plate next below.- So long as liquid .is present to the depth defined by the ange 81,' gas entering the openings 3l from below in escaping upwardly through the tower must pass through the layer of liquid which is present between the rim 32 and the depending serrated flange 33. 'I'he effect of this arrangement is to provide as in the usual manner a tortuous passageway through which gas escapes upwardly through a layer of liquid or aliquid film in passing each 0f the bubble plates. A constant ilood of liquid orator E by way 'of expansion valve 50. The line on the two lower plates in the bubble tower is assured lfrom a strong aqua return connection 39, while the four upper plates illustrated are always flooded with substantially anhydrous liquid ammonia from the pipe 4| discharging from the bottom of condenser C. s

The adjustment is such that no anhydrous liquid ammonia entering the pipe 4| can escape at the bottom of the tower, all of it being reevaporated to gaseous form before it reaches the discharge space 42 in the bottom of the tower. The supply of anhydrous liquid ammonia is, however, adequate to insure a minimum depth of liquid on the four topmost bubble plates or those which are disposed in the casing 24 above the strong aqua inlet 39. The two bottom bubble plates are similarly filled with liquidfrom the strong aqua connection 39 so that there is no possibility of any of the plates becoming dry, or of any ammonia and water vapor escaping upwardly through the tower from chamber y 42, without traversing the liquid illms provided by the bubble plates illustrated.

To simplify the drawings the bubble tower is I shown with two plates below and four above the strong aqua inlet, and these are more than are theoretically necessary. However, the tower is never 100% efficient and in practice three have been used below the strong-aqua inlet and six above, with excellent results. I

The bubble tower incorporated according to the teachings of the present invention, assures the escape of substantially water-free ammonia gas through the discharge connection 21 leading to thecondenser. The presence of anhydrous liquid ammonia on several of the bubble plates assists materially not only in dehydrating the ammonia gas coming from the generator,

vbut in reducing the temperature of that gas to substantially condensing temperature when it leaves the bubble tower. In other words, the

function of the anhydrous liquid ammonia con-v 52 leads to the absorber A.

Whereas it is usual to employ an absorber made up of a single drum, it is preferred, accord- .ing to the present invention, to embody this element in the form of several connected shells kin which the aqua is sprayed-over water cooled tubes. These shells are arranged in series to produce aqua kincreasing in concentration as it flows through the series. As' shown, the absorber shells are in vertically superposed relation and 'are supplied in parallel with ammonia gas from pipe 52, through pipes 56, 51 and 59. The weak aqua return pipe 59 leading from the exchanger H delivers weak aqua through parallel pipes 6I and 62 to spray pipes 60 in the top g of the flrst shell 53 of the absorber, thus the tubes in' the absorber are wetted with weak aqua. From the bottom of shell 53 it ows to spray pipes in the second shell 54, and similarly froml shell 54 to spray pipes in the shell 55, from which a strongaqua discharge connection 63 leads to the strong aqua ltank 64.

Tank 54 has a sight gage 65 and a discharge line 66 leading to the strong aqua pump P. Consequently, ammoniagas is supplied to each of the shells of the absorber, and there meets and is absorbed by the sprayed' aqua. The concentration increases progressively from top to bottom of the series of shells and reaches its maxil mum at the bottom of shell 55 where it disnection is to reduce the temperature of the esl caping ammonia gas, and at the same time assist in a thorough dehydration of the ammonia vapor discharged from the generator. 'I'he intermedie ate strong aqua return connection 39, serves to de-superheat the ammonia vapor passing upwardly throughv the tower and thus assists in the deposition of entrained water vapor. The net eifect of the connections 39 and 4I is to ensure the escape to the condenser of water-free or substantially water-free ammonia gas approximately at condensing temperature and free from superheat. The liquid ammonia def livered by the condenser is as nearly anhydrous as commercial liquid ammonia sold for refrigerating purposes.

The condenser C serves to liquefy the gas from tower T in the usual manner. While it is preferred that the condenser be of the shell and tube water cooled type, this is not essential. However, as shown the condenser comprises a shell 43 carrying water boxes 44 and 45 between glass 49. A discharge pipe 5I leads to the evapaqua and the vapor iowing to the absorber, anda deiinite diierential between the temperature charges into the strong aqua tank 64. The absorber shells are cooled by liquid supplied through inlet 43 which, after passing through water tubes in the'shells, is discharged at 40.

'I'he strong aqua pump P, preferably of the centrifugal type or driven by a rotary device such as a turbine, serves to supply the strong aqua to the heat exchanger H, here shown as comprising two shell and tube units 51 and B8, although ,a single unit may be substituted.

As is usual, the purpose of this exchanger is to increase the temperature of the strong aqua returning to-the generator, and to reduce the temperature of the weak aqua returning to the absorber by heat exchangebetween the two.

The weak aqua coming to the absorber from the generator surge drum passes through pipe 3 and through `the tubes ofthe shell and tube units 61 and 68, respectively, then through pipe 59 to the absorber. 'I'he strong aqua ows from tank 54 through pipe 66, pump P, pipe 1I, through shells 68 and 61 to pipe 12.

As indicated above, prior art systems have required manual adjustment of the strong aqua level in the system in accordance with changes of load and in accordance with changes in the supply of heat necessitated by changes of load. The present invention does 'away with such manual adjustments by providing automatic control of the system in order to produce and maintain a predetermined' ratio between the weak of refrigerant leaving the condenser and the temperature of vapor leaving the bubble tower.

Although numerous types of control may be used to carry out these functions, the diagrammatic illustration given herein includes pneumatically actuated control instruments which respond to the quantities above stated.

The rate at which liquid anhydrous ammonia is supplied to the tower through c, nection 4l should be controlled to maintain a c osen differential betweenthe vtemperature of liquid leaving the condenser and the temperature of ammonia vapor leaving the tower. In practice, it has been found that a temperature difference between these points of approximately 51 F. induces highly lsatisfactory operation. According- 1y there is disposed in the top of the tower, at 15, a thermal bulb leading' through a tube 18 to a differential controlling `instrument 11. A similar bulb 18 is associated with the liquid line 48 leading from the condenser C to the receiver R, and is connected through a tube 18 with the instrument 11. An air supply line 8| leads to the instrument 11, while a pneumatically actuated valve 82 interposed in liquid line 4| is controlled by instrument .11 through branch line 83. The instrument 11 which may be of any suitable known form operates to vary the air pressure in the branch line to maintain the desired 5 temperature difference between the points 18 and 18. Instruments of this type are well-known in the control art. A

The other automatically controlled factor is the relation of fiow rates between the gas discharged from evaporator E to the absorber and the weak aqua. delivered by pipe 58 to the top unit 53 of the absorber A. To effect this control a pneumatic instrument 84 connected to the air supply line 8| is provided and controls a pneumatically actuated valve 86 in line 58. The line 58 contains a measuring orifice 81 connected by two of surge drum l of the generator escapes through the pipe 8, passes through the exchanger and thence through pipe I8 to the top unit 58 of 'ate point in the, tower through pipe 88 and thence through strong aqua return 8 to surge -drum 5. The other circuit is from pipe 12 pressure transmitting ylines 88 and 88 to the instrument 84. Similarly, the line 52 leading from evaporator E to the absorber contains a measuring orifice 9| having separate pressure transmitting lines 82 and 83 leading to the instrument 84. The instrument 84 is of conventional construction and response to the pressure drops across the orifices to maintain an adjustment of valve 86 such that the flow of weak aqua to the absorber is coordinated with the' flow of ammonia v'apor from the evaporator. The mechanics of the control instrument are well known and are not a feature of this invention. The coordination of control rates is, however, novel and a feature of the invention.

The operation of the system as a whole is as l follows: The instruments 11 and 84 are adjusted in accordance with the temperature differential and relative ow rates which are to be maintained thereby, as above set forth. Then, as steam is supplied through the header 8, strong aqua circulation is induced in the generator surge drum and through the separate heaters or calandrias associated with it. A mixture of ammonia vapor and water vapor is discharged through connection 1 to the space 42 in the bottom of the tower T and this vapor- 4passes upwardly through the tower where it is deprived,

step by step, of its water vapor and superheat.

At the same time its temperature is lowered. The ammonia condenses as a liquid in` the condenser, a controlled portion of it being discharged through the line 4| to the top plate of tower T, and thence downwardly through the tower until it is all re-evaporated and passes upwardly and out through the discharge connection 21 as gaseous anhydrous ammonia. v

The major portion of the condensed liquid ammonia is discharged through pipe 48 to the.

receiver whence it flows through the expansion quired in the tower and provides excess through pipe 14 to the strong aqua header |8, or from pipe 18 directly to the surge drum by way of strong aqua return line 8.

The amount of liquid anhydrous ammonia returned to the topof the tower is controlled automatically by the instrument 11, as described. Similarly, the return of weak aqua to the top of the absorber is controlled bythe valve 88 in response to the now conditions affecting instrument 84. The rate of circulationof strong aqua is under the control of valve 84 which is regulated according tothe level of the aqua in the discharge end of surge drum 8.

When the level of liquid 'at the discharge end of the surge drum rises, the valve 84 tends to reduce the now through pipes 12, 88, and consequently also the flow through pipe 18 to the gen- Y erator and pipe 14 to the stron Mu header.A

The location of the valve 84 at a point beyon the heat exchangersprevents foaming of the liqy uid in the heat exchangers. "Ihe location of the valve.. 86 beyond the heat exchangers alsorprevents foaming. Elimination of foaming permits the use of small valves and ensures complete flooding of the exchangers. i

The adjustment of valve 88 preferably is such as to pass just sufncient strong aqua to absorb the heat capacity of the vapor entering tower T through line 1. This-permits the use 'of a tower T of minimum size, decreases the weir length refor ejector operation at the heaters.

The principles herein described bring about important results in simplicity of structure and efficiency of operation. The range of capacities valve to the evaporator E. There it takes up heat in the usualmanner and is discharged as ammonia gas throughthe connection l52 tothe absorber A. A I

The weak aqua formed in the discharge end is increased enormously so that for the first time it becomes practicable to operate an absorption system lof the ammonia-water type with automatic control giving substantially uniform eilicency, and increased flexibility in response to changing loads. The ammonia gas leaving the tower is so nearly anhydrous that purging of the system to remove water from the evaporator is practically never required.

What is claimed is:

` 1. In a refrigeration system ofthe absorption type, comprising a generator, a condenser, an absorber, an evaporator, and means for conveying refrigerant from the generator to the evaporator; a bubble tower interposed between the generator and .condenser and having a plurality of bubble plates, said tower serving both to rectify and to cool the ammonia vapor passing therethrough; means for supplying substantially anhydrous ammonia liquid from said condenser to said bubble tower adjacent the top thereof to flood certain of the plates with liquid ammonia; means for returning strong aqua from' said absorber to said generator; and supplemental strong aqua supplying means connecting the absorber and anintermediate point in said tower liquid 4 faqua. n

to flood the remainder of said plates with strong 2. 1nV an. absorption system yoi! refrigeration employing a lvolatile refrigerant and a volatile so1ventthereforand comprising a generator, an

said. evaporator; means for supplying substantower adjacent the top thereof to ood the liquid from the bottoniof the tower. y

tially pure refrigerant to ysaid evaporator, said means comprising a bubble tower interposed bejtween said generator and' said'condenser, a split return for strong refrigerant `solution from said absorber to anintermediate point in said bubble tower and to said generator, and a substantially `anhydrous liquidurefrigerant return from said condenser to the topl of said bubble tower.

3. In an absorption system of refrigeration employing ammonia and water, a generator; an absorber; a condenser; an evaporator; and means for supplying substantially pure ammonia to said evaporator; said means comprising a bubble tower interposed'between said generator and said 1condenser toboth rectify and cool thevvapors passing upwardly therein, a strong aqua return'from said absorber to an intermediate point in said tower and from said absorber to said generator, and a liquid ammonia return from said condenser to said tower at a point above said strong aqua return. Y

4.'.In an absorptionr'efrigeration system of the ammonia-water type, a source of strong aqua under pressure; a generator -comprising a plurality of aqual heating units connectedin parallel relation to one anotherand emptying into a common surge drum; means connected to said strong aqua source for causing circulation ofthe aquain said heating units; a bubble tower connected tothe gas outlet of said generator surge drum to rectify and cool the vapors passing u pwardly therein; an evaporator; an absorber; a condenserconnected between said towergand said evaporator and having a liquid 'ammonia discharge to the top of saidtower; means for deliveringgas from said evaporator to said absorber; and means for supplying strong aqua from saidabsorber. to lsaid generator in two branches one lof which leads to said tower between said liquid discharge from the condenser and the bottom ofthe tower, and the other of which leads directly to said surge drum.

5. In an absorption refrigeration system of the ammonia-water type, comprising a condenser, an evaporator, an absorber, agenerator and means for pumping strong aqua from the absorber to the generator, said generator comprising a surge drum fed by the strong aqua pumping means and having a plurality of parallel related units adapted to heat and circulate aqua of concentration which decreases from the point of strong aqua intake to said drum to the point of weak aqua discharge from said drum; a bubble tower including bubble plates,` said tower being interposed between the vapor oiftake of the generator and the condenser inlet and serving both to rectify and cool the ammonia vapor passing therethrough; means for supplying strong aqua to said tower at an intermediate point therein to flood the lower plates thereof; means for supplying strong aqua from the absorber tothe surge drum; means for supplying strong aqua to each of said units to cause ejector circulation of the liquid therein; and means for supplying substantially anhydrous ammonia liquid to said 6. In a refrigeration vsystem of the Aabsorption type, comprising a generator, a condenser, an absorber, an evaporator, and means for conveying refrigerant from the generator to the evaporator; abubble tower interposed between the generator andA condenser and having a plurality of bubble plates,said tower serving to rectify and to cool the ammonia vapors passing upwardly therethrough; means for supplying substantially anhydrous ammonia liquid vfrom said condenser to said bubble tower' adjacent the top thereof to flood certain of the plates with liquid ammonia; means for returning one portion of the strong aqua from the absorber to the generator; and means for supplying another portion `oi strong aqua to an intermediate pointv in said Abubble tower.

7. In arefrigeration system of the absorption type, comprising a condenser, an-absorber, an evaporator, and a generator for supplying 'gaseous refrigerant to said condenser, said generator having ejector liquid circulating means; a bubble tower interposed between the generator and condenser' and having a plurality of bubble plates,

said 'tower serving lboth to rectify and to cool substantially y to condensing ltemperature the ammonia vapors therein; means for supplying substantially anhydrous ammonia liquid from said `condenser to said bubble tower adjacent the top thereof to flood certain of the plates with liquid ammonia; means for returning one portion of the strong aqua from the absorber to the generator through said ejector liquid circulating means; and means for supplying another portion of strong aqua to an intermediate point in said tower.

' 8. In a refrigeration system of the absorption type, comprising a generator, a condenser, an absorber, an evaporator, `andmeans for conveying refrigerant from the generator to the evaporator; a bubble tower interposed between the generator and vcondenser and having a. plurality of bubble' for controlling the supply of said anhydrous am-A monia to said tower in accordance with the temperature diierential between the liquid ammonia flowing from the condenser and the ammonia vapor leaving the tower; and means for maintaining a predetermined ratio between the weak aqua and the ammonia vapor flowing to the absorber.

9. In a refrigeration system of the absorption type, comprising a generator, a condenser, an absorber, an evaporator, and means for conveying refrigerant from the generator to the evaporator; a bubble tower interposed between the generator and condenser and having a plurality of bubble plates, said tower serving vto rectify and to cool the ammonia vapors passing upwardly therethrough; means for supplying substantially anhydrous ammonia liquid from said condenser to said bubble tower adjacent the top thereof to flood certain of the plates with liquid ammonia;

means for returning one portion of the' strong aqua from the absorber to the generator; means for returning another portion of strong aqua `to an intermediate point in said bubble tower; automatic means responsive to the temperature differential between the liquid ammonia in the condenser and the ammonia vapor in the top of the tower for controlling the supply of anhydrous ammonia to the tower; and automatic means responsive to the rate of now of both the weak aqua and the ammonia vapor tothe absorber for controlling theA rate of iiow of said weak aqua.

10. In a refrigeration system of the absorption type comprising a generator, a condenser, an evaporator, means for delivering substantially anhydrous ammonia vapor from said generator to said condenser, and means Afor causing the ammonia to be delivered in liquid form to said evaporator; an absorber made up of a plurality of serially related spray type gas absorbing units; means for cooling `said units; means for deliver- .ing ammonia gas from said evaporator to each forl controlling the treatment of lthe anhydrous ammonia vapor leaving the generator in accordance with the-temperature differential between said vaporand the liquid ammonia leaving the condenser; and automatic means responsive to the rate of flow of both the weak aqua and the ammonia vapor to the absorber-for controlling the rate of flow of said weak aqua to said iirst unit. f

, 11. In a' refrigeration system of the absorption type comprising a generator, a condenser, an evaporator; means for delivering substantially anhydrous ammonia vapor from said generator to said condenser, and means for causing said vapor to be delivered in liquid form to said evaporator; an absorber comprising a plurality Aof said units, the arrangement being such that the units are maintained at successively lower temperatures in the direction of flow of the aqua; and means for delivering strong aqua from the last unit to said generator.

12. The combination dened, in claim 1l in which a single cooling medium and the aqua both pass serially through the units in counter ow relation. l I

13. In a refrigeration system of the absorption type comprising a generator, a bubble tower, a condenser, an evaporator; means for delivering substantially anhydrous ammonia vapor from said generator to said condenser by way of said bubble tower, and means for causing said vapor to be delivered in liquid form to said evaporator; an absorber comprising a plurality of surface heat exchange units; connections for delivering anhydrous ammonia vaporfrom the evaporator to said units in parallel; connections of low ow resistance for passing weak aqua derived from the generator, serially through said units and for fiowingit over the heat exchange surface in each of said units in directl absorbing relation with `the ammonia vapor, said vapor connections to the units being so constructedand arranged that the vapor entering the umts is free of resistance opposedfby aqua in the said units; connections `for supplying cooling medium for each of said units, the arrangement being such that the units are maintained at successively `lower temperatures in the direction of iiow of the aqua; and

means for delive strong aqua from the last unit of said absorber `to said generator, at least a part thereof passing throughsaid bubble tower.

. WALTER R, MCGINNIS. 

